1. Field of Invention
The present invention relates to an assembled battery monitoring device for an assembled battery in which a plurality of electric cells are connected in series that includes: a voltage measuring unit that detects a voltage of each electric cell by carrying out a setting operation for voltage measurement through wiring pulled from a positive terminal of each electric cell and a negative terminal of an electric cell on a lowest potential side; and a disconnection detecting unit that detects presence of disconnection in the wiring based on a detection voltage obtained by the setting operation for voltage measurement, as well as to a method of detecting disconnection in wiring for an assembled battery, and an assembled battery system.
2. Description of Related Art
Such an assembled battery monitoring device is a device for separately detecting a voltage of each of the electric cells that constitute the assembled battery.
As a technique of detecting a voltage of each electric cell, in addition to a technique, for example, of simply measuring a voltage of wiring between a positive terminal and a negative terminal of each electric cell (such as a technique using a difference amplifier or a resistance voltage dividing method), a technique of connecting a capacitor in parallel with each electric cell (see FIG. 5), and charging the capacitor once with the voltage of the electric cell, and then measuring the voltage of the charged capacitor, as described in JP-A-2001-56350 and JP-A-2002-204537, has been conceived of Incidentally, with the technique of measuring the voltage of the electric cell by means of the capacitor, it is possible to measure a value of the voltage of each electric cell in the same time.
When detecting the voltage of each electric cell as described above, disconnection of the wiring pulled from the assembled battery for voltage detection poses a problem. It should be noted that the disconnection as used herein indicates situations in which the wiring is electrically disconnected, including a case in which the wiring is actually cut as well as a case in which the wiring is electrically disconnected due to poor fitting of a socket that connects the wiring.
When such disconnection occurs in the wiring for voltage detection of the electric cells, for example, in the technique of charging the capacitor once with each of the electric cells, as the capacitors are connected in series, even when disconnection occurs in the wiring at a position indicated by “x” in FIG. 5, for example, capacitors Ca, Cb that are in serial connection are charged through adjacent electric cells Va, Vb that sandwich the disconnected portion, and thus voltages of the capacitors Ca, Cb that do not correctly represent the voltages of the electric cells Va, Vb, respectively, are detected.
In order to avoid such an erroneous detection, JP-A-2002-204537 employs a technique in which capacities of capacitors that are connected in series are changed accordingly from each other so that, when disconnection as described above occurs, a charging voltage of each capacitor varies between a case in which the wiring is normally connected and a case in which disconnection has occurred, and the occurrence of the disconnection can be detected based on a voltage difference. However, the technique of detecting the disconnection according to JP-A-2002-204537, the voltage difference between the detection voltage in the normal case and the detection voltage when the disconnection occurs is not sufficient, and therefore an improvement has been desired.
Additionally, while the above describes the problem when disconnection occurs taking an example in which the voltage of each electric cell is detected by means of the capacitor, a similar problem also occurs due to wiring disconnection when, for example, the voltage of each electric cell is directly measured using the voltage measuring unit.
Specifically, assuming that the capacitor as described above is replaced with an input impedance between detection voltage input terminals of the voltage measuring unit, there is a case that a voltage divided by the input impedance is detected. Further, the same problem also occurs when a capacitor for noise absorption is connected to the wiring from each of the electric cells to the voltage measuring unit.